1. Field of the Invention
The present invention relates to a sheet having contact plates used as a key switch for operating digital communication equipment such as portable phones, and the structure of a switch employing the same.
2. Description of the Prior Art
The structure of a conventional switch sheet is shown in FIGS. 6 to 8. FIG. 6 is an exploded perspective view showing the switch sheet. FIG. 7 is a plan view showing details of penetration holes. FIG. 8 is a side view of FIG. 7.
A conventional switch sheet comprises: a peel sheet 11 formed into a strip shape and having feed guide holes 11a provided at a fixed interval at both sides of a longitudinal direction X (feed direction); a rectangular spacer sheet 13 stuck to a separate face of the peel sheet 11 via an adhesive layer; and a rectangular upper face sheet 14 stuck to an upper face of the spacer sheet 13 via an adhesive layer.
On the peel sheet 11 and the spacer sheet 13, plural penetration holes 13a are formed which penetrate contact plates formed by expanding thin metal plates in a dome shape and make it possible to stick the dome tops of the contact plates to a lower face of the upper face sheet 14 via an adhesive layer. Coupling grooves 13b and 13c are provided to couple adjacent penetration holes 13a of the plural penetration holes 13a. 
The coupling grooves 13b and 13c are provided at about the center of the penetration holes 13a. By providing the coupling grooves 13b and 13c, when the dome-shaped contact plates are pushed, air within the domes can be expelled to other penetration holes 13a through the coupling grooves 13b and 13c, providing stable operability.
The coupling grooves 13b and 13c are formed from vertical coupling grooves 13c formed along the longitudinal direction X (feed direction) of the peel sheet 11 and the spacer sheet 13, and horizontal coupling grooves 13b formed along a direction Y crossing the longitudinal direction (feed direction).
However, in the structure of the above-described conventional switch sheet, the switch sheet is mounted on a circuit board in such a way that, while pulling out the stripe-shaped peel sheet 11 in the feed direction X, the peel sheet 11 is peeled off with the spacer sheet 13 and the upper face sheet 14 being overlaid, and the separated spacer sheet 13 and upper face sheet 14 are stuck onto the circuit board.
In this case, as shown in FIGS. 7 and 8, in the conventional switch sheet, since the coupling grooves 13b and 13c are formed at about the center of the penetration holes 13a, at both sides of the coupling grooves 13b and 13c, protrusions 13d exist toward a coupling part from an inner circumferential end of the penetration holes 13a. In the case where the coupling grooves 13b and 13c are formed in the direction Y crossing the longitudinal direction X (feed direction) of the peel sheet 11, since the protrusions 13d on a peel face between the spacer sheet 13 and the peel sheet 11 protrude from an inner circumferential end of the penetration holes 13a, the protrusions 13d remain unpeeled, so that it is difficult to peel the peel sheet 11 from the spacer sheet 13 in the vicinity of the protrusions 13. This has been a problem of the conventional switch sheet.
In the case where all the coupling grooves 13b and 13c are formed along the longitudinal direction X (feed direction) of the peel sheet 11, the position of the penetration holes 13a, that is, the layout of contact plates is limited. This has been another problem of the conventional switch sheet.
The present invention solves the above-described problems and provides a sheet having contact plates that allows a peel sheet thereof to be smoothly peeled from a spacer sheet and provides greater freedom in the layout of the contact plates, and a switch device employing the same.
To solve the above-described problems, a first embodiment of a sheet according to the present invention includes a strip-shaped peel sheet; a spacer sheet stuck onto the peel sheet via an adhesive layer; an upper face sheet stuck onto an upper face of the spacer sheet via an adhesive layer; and contact plates stuck to the upper face sheet. On the peel sheet and the spacer sheet, penetration holes through which the contact plates can penetrate, and coupling grooves by which the adjacent penetration holes are coupled are formed. The peel sheet is peeled off from a downstream end toward an upstream end of the peel sheet. Each of the coupling grooves has an upstream edge and a downstream edge where the upstream edge is positioned upstream with respect to the downstream edge. The coupling grooves are displaced toward the upstream end in the feed direction with respect to a center of each of the adjacent penetration holes so that there are no upstream edges within a plane of the spacer sheet, protruding toward the downstream end in the feed direction.
In a second embodiment of the invention, one side of the coupling grooves continues linearly or curvedly.
In a third embodiment of the invention, a coupling part at another side of the coupling grooves coupling the penetration holes is formed in an arc shape.
In a fourth embodiment of the invention, the spacer sheet and the upper face sheet are formed rectangularly and are mounted so that short sides of the rectangles are in the feed direction of the strip-shaped peel sheet, and wherein the penetration holes disposed at a side of a long side of the spacer sheet are coupled by the coupling grooves.
In a fifth embodiment of the invention, the coupling grooves are formed from first coupling grooves coupling the penetration holes disposed at the side of the long side of the spacer sheet and second coupling grooves coupling the penetration holes disposed at a side of the short side of the spacer sheet.
In a sixth embodiment of the invention, a sheet having contact plates including one of the first to fifth embodiments of the invention and a circuit board on which plural fixed contacts are disposed are provided. A peel sheet of the sheet having contact plates is peeled, and the sheet having the contact plates from which the peel sheet has been peeled is stuck onto the circuit board on which plural fixed contacts are disposed, by an adhesive layer of the spacer sheet so that the contact plates are opposite to the fixed contacts.